1. Field of the Invention
The invention relates to an apparatus for measuring the cylinder internal pressure of internal combustion engines and, in particular, of gas engines in this case, said apparatus having a first valve which opens into the cylinder interior space, having a measurement chamber which can be connected to the cylinder interior space and can be disconnected from the latter by means of the first valve, and having a pressure sensor which is arranged in the region of the measurement chamber in order to measure the pressure in the cylinder interior space when the first valve is open, with at least one second valve being provided in the region of the measurement chamber, said second valve being able to be changed to a closed position at least when the first valve is open in order to seal off the measurement chamber towards the outside.
2. The Prior Art
There is an increasing need in the construction of internal combustion engines to measure the cylinder internal pressure during operation. Such a measurement is performed by means of so-called indexing valves which comprise a pressure sensor in a measurement chamber which can be brought into connection with the cylinder internal space via a valve. There is a possibility of precise determination of knocking by means of such pressures sensors. It is also possible however to analyze the progression of combustion and to check cylinder balancing. Such indexing valves are known for example from EP 0 811 833 A or DE 29 39 324 A.
Especially in the case of gas engines there are special conditions which make it difficult to provide optimal configuration for such indexing valves. Gas engines are frequently used for electric power generation and are therefore in permanent operation, so that the exchange of the pressure sensor can only be performed in conventional indexing valves only after a longer running period in the course of routine maintenance. Until such an exchange is performed, the internal combustion engine must be operated without the functionality of pressure measurement. There is an additional problem in connection with gas engines that in contrast to internal combustion engines with auto-ignition (as is the case with diesel engines), the arrangement of an indexing valve remote from the combustion chamber is usually not possible because a thermal overload of the indexing valve and the indexing port would occur.
The present invention can also be applied to internal combustion engines which are not piston engines, e.g. to gas turbines. In this case, the terms “cylinder internal space”, “cylinder internal pressure”, etc. shall be understood mutatis mutandis as “combustion chamber”, “combustion chamber internal pressure”, etc.
Various indexing valves are further known from EP 0 811 832 A, DE 12 64 103 B and AT 235.046 B which comprise a pressure sensor and several valves. These indexing valves have a complex configuration and are thus difficult to produce and susceptible to malfunctions. As a result of the relatively long paths into the interior of the indexing valves, pressure peaks can be detected only imprecisely and there is an increased susceptibility to coking.
It is the object of the present invention to avoid such disadvantages and to provide a solution which has a simple configuration, is sturdy and enables a reliable measurement of the cylinder internal pressure. In particular, the indexing valve in accordance with the invention shall also enable continuous measurements over prolonged periods of time and enable an exchange of the pressure sensor during operation of the internal combustion engine.